C#——读文件方法（Filestream、File、StreamReader）

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OpenFileDialog fd = new OpenFileDialog();
            fd.Filter = "文本文件|*.txt";       //打开文件的类型
            if (fd.ShowDialog() == DialogResult.OK)
            {
                fn = fd.FileName;
                FileStream fs = new FileStream(fn, FileMode.Open, FileAccess.Read);
                int n = (int)fs.Length;
                byte[] b = new byte[n];
                int r = fs.Read(b, 0, n);
                textBox.Text = Encoding.Default.GetString(b, 0, n);
            }

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FileStream fs = new FileStream(fn, FileMode.Open, FileAccess.Read);
                long n = fs.Length;
                byte[] b = new byte[n];
                int cnt, m;
                m = 0;
                cnt = fs.ReadByte();
                while (cnt != -1)
                {
                    b[m++] = Convert.ToByte(cnt);
                    cnt = fs.ReadByte();
                }
                textBox.Text = Encoding.Default.GetString(b);

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textBox.Text = File.ReadAllText(fn, Encoding.Default);

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StreamReader sr = new StreamReader(fn, Encoding.Default);
                string line = sr.ReadLine();
                while (line != null)
                {
                    textBox.Text = textBox.Text + line + "rn";
                    line = sr.ReadLine();
                }

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StreamReader sr = new StreamReader(fn, Encoding.Default);
                textBox.Text = sr.ReadToEnd();